Speed control system for vehicle mounting a work performing device

ABSTRACT

A speed control system for a vehicle mounting a work performing device such as a trencher for controlling the speed of the vehicle inversely to the amount of work being performed by the work performing device. The vehicle includes a hydraulic drive motor and apparatus is provided for sensing the amount of work to be performed by the work performing device and for selectively controlling the flow of hydraulic fluid in a bypass for the hydraulic drive motor to thereby control the speed of the vehicle.

United States Patent 1191 Eaton 1 1 Aug. 7, 1973 1 SPEED CONTROL SYSTEMFOR VEHICLE MOUNTING A WORK PERFORMING DEVICE [75] Inventor: WilliamC.'Eaton, Omaha, Nebr.

[73] Assignee: Omsteel Industries, Inc., Omaha,

Nebr.

[22] Filed: Aug. 19, 1971 [21] Appl. No.: 173,025

52 US. Cl 173/8, 37/86, 37/010. 1,

37/DlG. 17, 91/412, 172/8, 173/24, 180/53 CD 51 1m. (:1 E021 5/06 [58]Field of Search 173/4-9,

173/24; 56/DIG. 37/DIG. l, DIG. 17, 86; /494; 91/412; 172/8; 180/53 CD,66, 105 R [56] References Cited UNITED STATES PATENTS 3,605,903 9/1971Glesmann 37/86 X 2,804,751 9/1957 Schroederm 173/8 2,136,921 11/1938 Joy..37/DIG.1

3,548,570 12/1970 Knott et a1 37/94 X 3,093,946 6/1963 Pitt et a1.56/DIG. 15

FOREIGN PATENTS OR APPLICATIONS 141,104 2/1961 U.SS.R.- 37/DIG. 1

Primary ExaminerRobert E. Pulfrey Assistant Examiner-Clifford D. CrowderAttorney-Alex A. Hofgren, Ernest A. Wegner et al.

[57 ABSTRACT 5 Claims, 2 Drawing Figures /66 6 14 if 1 I 1 76 vEH/c/EVEHICLE a i i I [Mg/ME PUMP 75 I Mam? 60 $56 Q2 Z rem/CHER 52 SPEEDCONTROL SYSTEM FOR VEHICLE MOUNTING A WORK PERFORMING DEVICE BACKGROUNDOF THE INVENTION Recent years have seen an increasing use of hydrostatictransmissions in various vehicles such as tractors or the like due tothe obvious advantage of their being settable to an infinite number ofspeeds. Such a characteristic is of particular advantage in thatvehicles which bear a work performing means such as a trenching devicewhich will normally be moved across the ground at as fast a rate aspossible without overloading the work performing means. Thus, where theload is relatively constant, the speed of the vehicle may be set withcomplete precision.

However, very few situations are encountered in practice where the loadfor such work performing means remains relatively constant. For example,in trenching applications, the nature of the ground in which a trench isbeing dug will vary from time to time and even if the same does notappreciably vary, when the boom of a trencher is maintained at aconstant attitude with respect to the vehicle, a change in the terrainmay tend to cause the boom to dig in to the ground thereby increasingthe amout of work required.

SUMMARY OF THE INVENTION It is the principal object of the invention toprovide a new and improved speed control system for vehicles mountingwork performing means as a trencher for controlling the speed of thevehicle inversely with the work to be performed by the work performingmeans. More particularly, it is an object of the invention to providesuch a speed control system for a vehicle employing a hydrostatictransmission.

The exemplary embodiment of the invention achieves the foregoing in avehicle having ground engaging propulsion means driven by a hydraulicmotor receiving hydraulic fluid under pressure from a hydraulic pump,both normally forming part of a conventional hydrostatic transmission.According to the invention, a bypass line about the hydraulic motor isestablished and the flowrate through the same is varied according to theamount of work being required of a work performing means carried by thevehicle and adapted to be operated as the vehicel moves acrossthe'ground or the like.

According to one embodiment, the amount of work to be performed by awork performing meanssuch as a trencher, is determined by sensing thepressure between the hydraulic pump and the hydraulic motor of thevehicle, it being recognized that as the work to be performed by atrencher increases, an increased drag will be placed upon the vehicleresulting in a buildup of pressure on the high pressure side of thehydraulic motor. A sensed increase in pressure is then employed todecrease the speed of the hydraulic motor and thus the speed of thevehicle. Specifically, a hydraulic fluid bypass is established inparallel with the hydraulic motor and in the line is an overflow valveof the type that will remain closed until a predetermined pressuredifferential across the same exists, at which time it will open.According to the preferred embodiment, the pressure at which such valvewill open may be adjusted and when the same opens, the bypass route isestablished for hydraulic fluid under pressure causing the by draulicmotor to slow down thereby decreasing the speed of the vehicle.

In addition, the bypass line may include a bypass control valve whichmay be responsive to operation of the trencher or other work performingdevice to activate the bypass line. According to one embodiment, thebypass control valve is a piston operated valve connected to the highpressure side of a hydraulic motor for the trencher and operable to openwhen normal digging pressures upstream of the trencher motor exist.

Other objects and advantages will become apparent from the followingspecification taken in conjunction ,with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a vehicleembodying a speed control system made according to the invention; and

FIG. 2 is a schematic of the speed control system.

DESCRIPTION OF THE PREFERRED EMBODIMENT A speed control system accordingto the invention is embodied in an articulated vehicle having a firstframe, generally designated 10, and a second frame, generally designated12. Included on the first frame 10 is a power plant 14 which drives aplurality of hydraulic pumps in cluding a conventional hydraulic pistonpump 16. Additionally associated with the first frame 10 is a steeringmeans 18 and a namually operable speed control means 20.

Both .of the frames 10 and 12 mount the wheels 22 onv axles 24associated with respect to differentials 26 and 28. The differential 26receives rotary power via drive shaft 30 which is coupled by a universaljoint 32 to the differential 26 and a universal joint 34 to a hydraulicmotor and transmission 36 which is driven by the piston pump 16. Thehydraulic motor and transmission 36 is connected by meansof a universaljoint 38 to provide rotary power to the differential 28. i

As illustrated in FIG. 1, the forward end of the first frame mounts plowmeans 40 which form no part of the present invention while the secondframe 12 mounts a trenching apparatus, generally designated 42.

While in the exemplary embodiment, the trencher 42 is shown as'a' workperforming means mounted on the vehicle, as will become apparenthereinafter, the invention is not so limited. For example, the workperforming means could be most any type of device which performs work asthe vehicle moves along the ground and which will increase the drag onthe vehicle as work requirements increase.

In any event, the work performing means in the form of the trencher 42comprises a boom 44 which is mounted on a shaft 46 which in turn ispivotally mounted on the second frame 12. Various idler means 48 supporta trenching chain 50. Additionally, there are provided augers S2 forclearing excavated material away from the trench when the trenchingdevice is pivoted about the axis provided by the shaft 46 to a trenchingposition. A drive for the chain 50 is provided by a driven sprocket 54which is driven by a hydraulic motor 56.

With reference to FIG. 2, the speed control system will now bedescribed. The same takes advantage of the wellknown fact that as theload on a hydraulic motor increases, the pressure will increase at theinlet or high pressure side thereof. Thus, the high pressure side of ahydraulic drive motor will be a measure of the work requirements imposedupon the same by work performing means that it is driving.

As can be seen, the power plant 14 drives not only the hydraulic pistonpump 16, but a hydraulic pump 58 as well which provides hydraulic fluidunder pressure for the trencher motor 56.

The high pressure line from the vehicle pump 16 to the hydraulic motorand transmission 36 is designated 60 while the return, or low pressureline, is designated 62. Bypassing the hydraulic motor and transmission36 is a bypass line, generally designated 64, and which is composed ofan adjustable overflow valve 66 in series with a pilot operated bypasscontrol valve 68. Assuming for the moment that the valve 68 is in anopen condition, the pressure at which the bypass line 64 .will begin topass hydraulic fluid under pressure may be selectively controlled bysuitable adjustment of the adjustable overflow valve 66. Thus, if thepressure in the line 60 is below that required to open the valve 66, thebypass line 64 will not pass fluid under any circumstances so that thepressure setting of the valve 66 sets a minimum pressure at which theline may become effective thereby setting a minimum speed for thevehicle at which the bypass may become effective.

The control valve 68 includes a valve seat 70 and a valve member 72. Theoutlet 74 of the valve 68 is connected to the low poressure line 62 tocomplete the bypass path and a piston rod 76 having a piston 78 on oneend is connected to the valve member 72 to serve as an operator for thesame. A spring 80 is provided to normally bias the valve member 72towards a closed position. Suitable seals (not shown) carried by thepiston 78 and surrounding the rod 76 to the left of the outlet 74respectively isolate the left side of the piston and the outlet 74 fromthe right side of the piston 78. To open the valve 68, hydraulic fluidunder pressure is applied against the piston 78 whereupon the same willmove against the bias of the spring 80 and carry the valve member 72away from the valve seat 70.

To apply pressure to the piston 78, there is provided a line 82connected to the high pressure line 86 for the trencher hydraulic motor56. The line 82 serves as a means for sensing when the trencher isoperating by conveying the pressure at the high pressure side of thetrencher hydraulic motor 56 to the piston 78 to ultimately move thevalve member 72 away from the seat 70 to activate the bypass line tocontrol vehicle speed.

With the foregoing construction in mind, the manner of operation will bedescribed. It will be recognized that the speed of the vehicle motor 36and thus the vehicle speed will be proportional to the volume of oilcirculated in the hydraulic loop per unit of time. The torque thehydraulic motor 36 develops will be proportional to the fluid pressuredifferential across the motor 36. The speed control system describedabove introduces a modifying factor into the effect of pressuredifferential which is seen by the hydraulic motor 36 to ultimatelycontrol vehicle speed.

In a typical installation, the components are arranged such that thebypass control valve 68 will open at, for example, 500 psi to activatethe bypass line. Those skilled in the art will recognize that duringnormal trencher operations, pressure in the line 86 will exceed 1,000psi. Thus, for normal operation of the trencher, the bypass line will beactivated.

The valve 66 will be set to open at pressures in excess of somepredetermined value. Normally, the setting will be such that thehydraulic motor 36 will be permitted to develop sufficient torque toforce the trencher into the soil at a rate which will requiresubstantially full horse power output of the engine 14. In a tpicalcase, a 450 psi setting will serve the purpose. Thus, as the trencherencounters harder digging or unevenness of terrain causes the trencherto bite more deeply into the ground, there will be a corresponding riseis pressure in the line 60 due to the increased drag on the vehicle andthe hydraulic motor 36. The valve 66 will open to permit fluid to bypassthe motor 36 thereby slowing the machine temporarily to permit thetrencher to clear itself.

One special advantage of the system is due to the fact that the pressuredrop across the valve 66 will be in proportion to the flow rate ofhydraulic fluid through the same. Thus, it is possible to select apressure setting for the valve 66 for average conditions whilepermitting an increase in effective pressure across the hydraulic motor36 by increasing the flow of hydraulic fluid from the pump 16. Thus, asystem providing field flexibility which enjoys the inherent reliabilityof a relief valve is provided.

I claim 1. In a vehicle having ground engaging propulsion means and avariable speed hydraulic motor for driving the same, a hydraulic pumpfor providing hydraulic fluid under pressure to the vehicle motor, awork performing means adapted to perform work as the vehicle moves alongthe ground, the improvement comprising: means for sensing the amount ofwork to be performed by the work performing means and for establishing ahydraulic fluid bypass about said hydraulic motor when the amount ofwork to be performed by the work performing means increases to decreasethe speed of the vehicle.

2. The invention of claim 1 wherein said sensing and establishing meanscomprises a hydraulic conduit in parallel with said vehicle motor andvalve meaiis in said conduit; said valve means being operable to openwhen a predetermined pressure differential exists across the same.

3. The invention of claim 2 further including a control valve in saidconduit; and means for opening said control valve when said workperforming means is operative.

4. The invention of claim 2 wherein said valve means is adjustablewhereby the pressure differential necessary to cause the same to openmay be selectively varied. Y

i 5. A vehicle comprising: a frame; propulsion means mounted on saidframe; a hydraulic vehicle drive motor connected to said propulsionmeans and operable when energized to cause said vehicle to move; asource of hydraulic fluid under pressure; means connecting said sourceto said hydraulic motor; work perfonning means connected to said frameto be movable with said vehicle and to perform work while said vehicleis moving; drive means for said work performing means including ahydraulic work performing motor adapted to receive hydraulic fluid underpressure; and vehicle speed control means comprising a bypass lineacross said hydraulic vehicle drive motor including an overflow valvefor controlling the flow rate of hydraulic fluid through said bypassline, a bypass control valve in series therewith, and means connected tothe high pressure side of said hydraulic work performing motor forsensing the pressure thereat and for opening said bypass control valveto permit diversion of hydraulic fluid from said hydraulic vehicle drivemotor to thereby control the speed of the same and the speed of thevehicle.

1. In a vehicle having ground engaging propulsion means and a variable speed hydraulic motor for driving the same, a hydraulic pump for providing hydraulic fluid under pressure to the vehicle motor, a work performing means adapted to perform work as the vehicle moves along the ground, the improvement comprising: means for sensing the amount of work to be performed by the work performing means and for establishing a hydraulic fluid bypass about said hydraulic motor when the amount of work to be performed by the work performing means increases to decrease the speed of the vehicle.
 2. The invention of claim 1 wherein said sensing and establishing means comprises a hydraulic conduit in parallel with said vehicle motor and valve means in said conduit; said valve means being operable to open when a predetermined pressure differential exists across the same.
 3. The invention of claim 2 further including a control valve in said conduit; and means for opening said control valve when said work performing means is operative.
 4. The invention of claim 2 wherein said valve means is adjustable whereby the pressure differential necessary to cause the same to open may be selectively varied.
 5. A vehicle comprising: a frame; propulsion means mounted on said frame; a hydraulic vehicle drive motor connected to said propulsion means and operable when energized to cause said vehicle to move; a source of hydraulic fluid under pressure; means connecting said source to said hydraulic motor; work performing means connected to said frame to be movable with said vehicle and to perform work while said vehicle is moving; drive means for said work performing means including a hydraulic work performing motor adapted to receive hydraulic fluid under pressure; and vehicle speed control means comprising a bypass line across said hydraulic vehicle drive motor including an overflow valve for controlling the flow rate of hydraulic fluid through said bypass line, a bypass control valve in series therewith, and means connected to the high pressure side of said hydraulic work performing motor for sensing the pressure thereat and for opening said bypass control valve to permit diversion of hydraulic fluid from said hydraulic vehicle drive motor to thereby control the speed of the same and the speed of the vehicle. 